METHOD OF INCREASING THE LOW SHEAR RATE VISCOSITY AND SHEAR THINNING INDEX OF DIVALENT CATION-CONTAINING FLUIDS AND THE FLUIDS OBTAINED THEREBY

摘要

Disclosed is a method of increasing the low shear rate viscosity and th e shear thinning index of aqueous fluids containing a divalent ration salt, a crosslinked amylopectin starch which functions as both a viscosifier/suspending agent and as a fluid loss control additive, and a bridging agent, the fluids resulting from the method, and the use of the fluids in drilling a well, wherein the bridging agent is a sized particulate magnesium carbonate or a mixture of sized magnesium carbonate and sized calcium carbonate. The median (D50) particle size of the magnesium carbonate is from about 2 .mu.m to about 10 .mu.m. The weight rati o of calcium carbonate to magnesium carbonate is from about 70/30 to about 0/100.